Why does salt displace water?

Question

I was assigned a science project just last week. I have to get 2 of the same plants and water one with salt water and the other with fresh water. I need a hypothesis. I think that the plant without salt will grow taller. My brother told me that is true, because the salt displaces the water. But i need to know if this info is correct, and what i should put in my hypothesis. I am really, really stuck!

If you have any other ideas, please tell me what you think my hypothesis should be!!!!

Answer 1

Your hypothesis is OK, and I presume you will design an experiment to help confirm or refute your hypothesis.

Your brother agreed with your hypothesis, and then offered another hypothesis of his own. Ask him to clarify, so that you understand what he means. Then, put that into the form of a hypothesis that can be tested, and decide whether you want to test his in addition to testing yours.

Here's an example. You get the plants. Water them both with pure water until the water starts to run out of the bottom of the pot. Then check them every day. When you stick your finger half an inch or so into the pot and it's dry, it's time to water again. Add water a little at a time, until it just starts to run out the bottom. Let's say you discover that the plants, at this stage of development, need 5 ounces of water every 4 days.

If you water them every 4 days with 5 ounces of pure water vs. 5 ounces of salt water, you will test your hypothesis.

If you instead water with 5 ounces of pure water vs. 5 ounces of pure water plus salt, you will test both.